Method for catalytically synthesizing dimethyl carbonate based on novel solid base

Abstract

The invention discloses a method for catalytically synthesizing dimethyl carbonate based on a novel solid base, which specifically comprises the following steps: loading KF on a magnesium-iron mixed oxide carrier, calcining at high temperature to obtain the solid base with higher alkalinity, and carrying out ester exchange reaction on ethylene carbonate and methanol by using the solid base as a catalyst to obtain dimethyl carbonate. When the dosage of the catalyst is 0.1-5% of the mass of the ethylene carbonate and the molar ratio of the methanol to the ethylene carbonate is 4-16, the reaction is carried out for 0.5-3 hours under the reflux condition, and the dimethyl carbonate can be synthesized with high yield and high selectivity. The preparation process has the advantages of simplicity in preparation, easiness in separation, high activity and reusability.

Description

Technical Field

[0001] The present invention relates to a method for synthesizing dimethyl carbonate, in particular to a method for preparing dimethyl carbonate by transesterification of ethylene carbonate and methanol catalyzed by a novel solid base. Background Art

[0002] Dimethyl carbonate (DMC for short) is a low-toxicity solvent and reaction reagent widely used in the chemical industry and is recognized as a green chemical reagent by the European Union. In the field of battery manufacturing, DMC can be used as an electrolyte for lithium-ion batteries. At the same time, due to its relatively high oxygen content and octane number, DMC can replace methyl tert-butyl ether as a gasoline additive to improve the anti-knock performance of gasoline.

[0003] At present, the methods for synthesizing dimethyl carbonate mainly include methanol oxidative carbonylation, urea alcoholysis, direct reaction of methanol with CO2, and transesterification of ethylene carbonate or propylene carbonate with methanol, etc. In the oxidative carbonylation reaction of methanol, the formation of by-product H2O will cause catalyst deactivation, and O2 as a reactant, there is a risk of explosion in this reaction system in the presence of CO. The reaction conditions of the urea alcoholysis route are relatively harsh, the single-pass conversion rate is low, and there are also problems such as urea decomposition and nitrogen-containing compounds generated by the decomposition reaction affecting the quality of DMC. The direct synthesis of DMC from CO2 and methanol has a high atom utilization rate, but this reaction is restricted by the thermodynamic equilibrium, the reaction conditions are harsh, and the requirements for the stability and activity of the catalyst are relatively high. At present, the industrial production of DMC mainly relies on the transesterification reaction of ethylene carbonate or propylene carbonate with methanol. This reaction route has the characteristics of cheap and easily available raw materials, mild reaction conditions, high yield, etc. In addition, the co-produced ethylene glycol or propylene glycol is also a raw material for producing polyester fibers and films. Therefore, the transesterification method is considered a green DMC production route and is widely used.

[0004] At present, in the process of preparing DMC by transesterification, the catalysts that can be used include acidic catalysts and basic catalysts. Among them, acidic catalysts include inorganic acid H2SO4, organic carboxylic acids, organic sulfonic acids, etc. However, the transesterification reaction catalyzed by acids generally has low DMC yield and selectivity, and by-products such as dimethyl ether and ethylene glycol monomethyl ether are easily generated in the system. Basic catalysts are widely used in the transesterification reaction of ethylene carbonate or propylene carbonate with methanol. The most commonly used are basic hydroxides, basic carbonates, and organic bases such as CH3ONa and CH3OK (M.S. Han, B.G. Lee, B.S. Ahn, K.Y. Park and S.I. Hong, React. Kinet. Catal. Lett., 2001, 73, 33-38.). However, the above homogeneous catalysts need to be separated after the reaction, and incomplete separation is likely to cause fouling of the reboiler at the bottom of the distillation column, affecting the continuity of operation. Basic ionic liquid catalysts have the advantages of good solubility and thermal stability, can be enriched in the bottom of the column and reused during the product distillation separation process without additional separation operations ((a) H.Y. Ju, M.D. Manju, D.W. Park, Y. Cboe and S.W. Park, React. Kinet. Catal. Lett., 2007, 90, 3-9. (b) Z.Z. Yang, L.N. He, X.Y. Dou and S. Chanfreau, Tetrahedron Lett., 2010, 51, 2931-2934. (c) Y. Song, X. He, B. Yu, H.R. Li and L.N. He, Chin. Chem. Lett., 2022, 31, 667-672.), but the synthesis process of ionic liquids is complex, the cost is high and they have potential environmental toxicity.

[0005] Compared with homogeneous basic catalysts, solid bases are easy to separate from the system, so they are the current research focus in the synthesis of dimethyl carbonate by transesterification. Commonly used solid base catalysts include metal oxides and their mixtures, supported ionic liquid catalysts, solid base catalysts based on the formation of active new species through solid-phase reactions, etc. Among many metal oxide catalysts, CaO and MgO are inexpensive and easily available, and have relatively high basicity, so they are relatively ideal solid base catalysts. However, because they are easy to react with methanol and the generated ethylene glycol in the reaction system to form alcoholates and partially dissolve in the reaction system or adhere to the surface of the solid catalyst, Ca 2+ 、Mg 2+Problems such as loss, product contamination, and difficulty in filtering residual catalysts ((a) Z.W. Song, B. Subramaniam and R.V. Chaudhari, Ind. Eng. Chem. Res., 2018, 57, 14977 - 14987. (b) Z.M. Cui, Z. Chen, C.Y. Cao, W.G. Song and L.J. Jiang, Chem. Commun., 2013, 49, 6093 - 6095.) have led to the preparation of CaO / Al2O3, MgO / Al2O3 (E.S. Umdu, M. Tuncer and E. Seker, Bioresource Technol., 2009, 100, 2828 - 2831.), CaO / ZnO (A.C. Alba-Rubio, J. Santamaría-González, J.M. Mérida-Robles, R. Moreno-Tost, D. Martín-Alonso, A. Jiménez-López and P. Maireles-Torres, Catal. Today., 2010, 149, 281 - 287.), CaO / ZrO2 (H. Wang, M. Wang, S. Liu, N. Zhao, W. Wei and Y.H. Sun, J. Mol. Catal. A-Chem., 2006, 258, 308 - 312.) by loading them on inert matrices. Although the problem of difficult catalyst filtration can be solved, the loss of active components still exists. Transition metal oxides with basicity and their mixed metal oxides have also been used in this transesterification reaction, including CeO2 (J. Xu, K.Z. Long, F. Wu, B. Xue, Y.X. Li and Y.C. Cao, Applied Catalysis A: General., 2014, 484, 1 - 7.), Ce-La mixed oxides (P. Kumar, V.C. Srivastava and I.M. Mishra, Catal. Commun., 2015, 60, 27 - 31.), etc. However, due to their relatively weak basicity, relatively high reaction temperatures and pressures are generally required to achieve a high DMC yield, increasing the operation and equipment costs.

[0006] Loading alkaline ionic liquids on inert porous support materials can obtain solid base catalysts with high activity, but there is still a problem of ionic liquid loss. Fixing ionic liquids to support materials through covalent bonds requires a more complex preparation process ((a) K.H. Kim, D.W. Kim, C.W. Kim, J.C. Koh and D.W. Park, Korean J. Chem. Eng., 2010, 27, 1441 - 1445. (b) J.Q. Wang, J. Sun, W.G. Cheng, C.Y. Shi, K. Dong, X.P. Zhang and S.J. Zhang, Catal. Sci. Technol., 2012, 2, 600 - 605. (c) CN202310360367 (d) CN201410327843).

[0007] In recent years, solid bases formed by solid - phase reactions between two components at high temperatures have also been used in the transesterification method for preparing DMC. For example, a transition - metal Fe - modified Mg - Al mixed oxide synthesized by the co - precipitation method combined with high - temperature calcination has a high surface basicity density and exhibits good catalytic activity. The conversion rate of PC is 66.2%, and the selectivity of DMC can reach 82.6% (Q. Wang, F. Li, H.H. Zhao, Z.Q. Kuang, F. Wang, L. Li, N. Zhao and F.K. Xiao, J Fuel Chem Technol., 2020, 48, 448 - 455.); KF is loaded onto neutral Al2O3 by the impregnation method and undergoes a solid - phase reaction through high - temperature calcination to generate a new active species K3AlF6, which has high catalytic activity. Under the optimal conditions, the conversion rate of PC is 70.9%, and the selectivity of DMC is higher than 98%, but there is a problem of poor catalyst stability. When the catalyst is used for the second time, the conversion rate of PC is only 24.7% (C. Murugan, H.C. Bajaj and R.V. Jasra, Catal. Lett., 2010, 137, 224 - 231.); A new solid base Li / NaY is prepared by the solid - phase reaction between NaY zeolite and Li2CO3 at high temperatures, which has higher basicity than NaY. The yield of DMC reaches 89%, and the selectivity reaches 99%, with good reusability. However, the hot - filtration experiment shows that there is a relatively large amount of Li + in the solution, and there is a small loss of catalyst mass (M. Yang, H.R. Li and L.N. He, Asian J. Org. Chem., 2022, 11, e202200224.).

[0008] Although there have been extensive discussions on the application of heterogeneous catalysts in the transesterification reaction of ethylene carbonate and methanol, there are still some problems at present, including poor stability of heterogeneous catalysts with high catalytic activity, relatively low single-pass conversion of catalysts with relatively good stability, and the need for high-temperature and high-pressure reaction conditions. In addition, the complex preparation process is also one of the reasons limiting the industrial application of heterogeneous catalysts. Therefore, it is necessary to develop heterogeneous catalysts with good stability, high activity and simple preparation methods for the synthesis of DMC by transesterification. Summary of the Invention

[0009] The present invention aims to provide a method for catalytic synthesis of dimethyl carbonate based on a novel solid base. The solid base catalyst has the advantages of simple preparation, high catalytic activity, good stability and easy separation from the reaction system. The implementation process of the present invention is as follows:

[0010] Preparation of solid base catalyst: Magnesium chloride hexahydrate and ferrous sulfate heptahydrate with a molar ratio of 1:0.5 - 2 are fully dissolved in deionized water, and a sufficient amount of sodium oxalate solution is added dropwise thereto under stirring conditions to precipitate metal ions. After filtration, the precipitate is washed thoroughly with distilled water. After the precipitate is fully dried, a certain amount of KF methanol solution is added to the obtained solid, so that the mass of KF contained therein is 10 - 30% of the precipitate. After full mixing and aging, methanol is removed by a suitable method, and then calcined at 200 - 700 °C for 0.5 - 5 h to obtain the solid base catalyst.

[0011] When synthesizing dimethyl carbonate, a solid base catalyst prepared by the above method with a mass of 0.1 - 5% of the mass of ethylene carbonate is added to the reaction system, and ethylene carbonate and methanol are added in a molar ratio of 1:4 - 16, and the reaction is carried out for 0.5 - 3 h under reflux conditions. The reaction system is cooled to room temperature, and the solid catalyst and the reaction solution are separated by filtration.

[0012] Compared with other solid base catalysts, this catalyst has a simple preparation process, easily available raw materials, and has high activity and selectivity for DMC synthesis, can be separated by simple filtration, and the catalyst has good stability during repeated use. Detailed Embodiments

[0013] Example 1 Preparation of the carrier iron-magnesium oxide and evaluation of its catalytic activity

[0014] A method for catalytic synthesis of dimethyl carbonate based on a novel solid base, the steps are as follows:

[0015] 1) Keep the total molar amount of magnesium chloride hexahydrate and ferrous sulfate heptahydrate at 30 mmol, adjust their molar ratio between 1:0.5 and 2, dissolve them in 100 mL of deionized water. After complete dissolution, add 100 mL of 0.3 M sodium oxalate aqueous solution dropwise thereto to form a precipitate. Filter and collect the precipitate, wash it thoroughly with distilled water, vacuum dry it at 60 °C for 12 h, and calcine it in a muffle furnace at 400 °C for 1 h to obtain an iron-magnesium mixed oxide;

[0016] 2) Take 300 mg of the above-mentioned iron-magnesium mixed oxide as a catalyst, add 6 g (68.14 mmol) of ethylene carbonate and 22 mL (545 mmol) of methanol to a 100 mL round-bottom flask equipped with magnetic stirring and a reflux tube, heat to reflux, and react for 2 h. After the reaction is completed, when the reaction system cools to room temperature, take 1 mL of the reaction solution, filter it through a membrane, add 10 mL of methanol, and analyze the yield and selectivity of dimethyl carbonate by gas chromatography.

[0017] Table 1 Influence of the composition of the iron-magnesium mixed oxide on the yield and selectivity of dimethyl carbonate

[0018]

[0019] It can be seen from the data in Table 1 that when the magnesium-to-iron molar ratio increases, that is, when the magnesium content increases, the yield and selectivity of dimethyl carbonate gradually increase. The reason is that magnesium oxide has higher basicity and undergoes a solid-phase reaction with iron oxide at high temperature to generate more basic species, while iron oxide mainly serves as the structural framework of the catalyst to improve the stability of the catalyst. Therefore, the preferred carrier composition has a magnesium-to-iron molar ratio of 2:1.

[0020] Example 2 Influence of KF loading on the catalytic effect

[0021] A method for catalytic synthesis of dimethyl carbonate based on a novel solid base is as follows:

[0022] 1) Dissolve 4.07 g (20 mmol) of magnesium chloride hexahydrate and 2.78 g (10 mmol) of ferrous sulfate heptahydrate in 100 mL of deionized water. After complete dissolution, add 100 mL of 0.3 M sodium oxalate aqueous solution dropwise thereto to form a precipitate. Filter and collect the precipitate, wash it thoroughly with distilled water, vacuum dry it at 60 °C for 12 h, and calcine it in a muffle furnace at 400 °C for 1 h to obtain 2.1 g of a catalyst support, iron-magnesium oxide;

[0023] 2) Add a certain amount of KF methanol solution (the mass of KF is 10 - 30% of the mass of the support) to the obtained solid, ultrasonically mix it thoroughly, let the slurry stand for 6 h, rotary evaporate to remove methanol, vacuum dry it overnight at 100 °C, and calcine it in a muffle furnace at 400 °C for 1 h to obtain a solid base catalyst;

[0024] 3) 300 mg (5 wt.%) of the catalyst, 6 g (68.14 mmol) of ethylene carbonate, and 22 mL (545 mmol) of methanol were added to a 100 mL round-bottom flask equipped with magnetic stirring and a reflux tube, heated to reflux, and reacted for 2 h. After the reaction ended and the reaction system cooled to room temperature, 1 mL of the reaction solution was filtered through a membrane filter, 10 mL of methanol was added, and gas chromatography analysis was performed.

[0025] Table 2 Effects of Different Loadings on the Yield and Selectivity of Dimethyl Carbonate

[0026]

[0027] It can be seen from the data in Table 2 that when KF was loaded onto the catalyst support, the yield and selectivity of dimethyl carbonate increased significantly. The reason is that a solid-phase reaction occurred between KF and the support at high temperature, generating a species with stronger alkalinity. However, the loading amount of KF had no significant effect on the catalytic activity. Therefore, the preferred loading amount of KF was 10 - 30% of the mass of the support.

[0028] Example 3 Effect of Calcination Temperature on the Catalytic Effect

[0029] A method for catalytic synthesis of dimethyl carbonate based on a novel solid base is as follows:

[0030] 1) 4.07 g (20 mmol) of magnesium chloride hexahydrate and 2.78 g (10 mmol) of ferrous sulfate heptahydrate were dissolved in 100 mL of deionized water. After complete dissolution, 100 mL of 0.3 M sodium oxalate aqueous solution was added dropwise thereto to produce a precipitate. The precipitate was collected by filtration, washed thoroughly with distilled water, dried in vacuo at 60 °C for 12 h, and calcined in a muffle furnace at 400 °C for 1 h to obtain 2.1 g of the catalyst support.

[0031] 2) A certain amount of KF methanol solution (the mass of KF was 20% of the support) was added to the obtained solid, and it was ultrasonically mixed thoroughly. The slurry was allowed to stand for 6 h, methanol was removed by rotary evaporation, dried in vacuo at 100 °C overnight, and calcined at 200 - 700 °C in a muffle furnace for 1 h to obtain approximately 1.8 g of the solid base catalyst.

[0032] 3) 300 mg (5 wt.%) of the catalyst, 6 g (68.14 mmol) of ethylene carbonate, and 22 mL (545 mmol) of methanol were added to a 100 mL round-bottom flask equipped with magnetic stirring and a reflux tube, heated to reflux, and reacted for 2 h. After the reaction ended and the reaction system cooled to room temperature, 1 mL of the reaction solution was filtered through a membrane filter, 10 mL of methanol was added, and gas chromatography analysis was performed.

[0033] Table 3 Effects of Different Calcination Temperatures on the Yield and Selectivity of Dimethyl Carbonate

[0034]

[0035] The calcination temperature affects the solid-phase reaction between KF and the catalyst support, thereby changing the basicity of the catalyst support. It can be seen from the data in Table 3 that the catalytic activity increases with the increase of the calcination temperature. It should be noted that since KF and the support itself also have Lewis basicity, the uncalcined catalyst also exhibits mild catalytic activity, but this catalyst is easily dissolved out during repeated use, and the activity in the second use is only 80% of that of the newly prepared catalyst. Therefore, the calcination temperature in the catalyst preparation is preferably 200-700 °C, and more preferably 400-600 °C.

[0036] Example 4 Influence of Calcination Time on Catalytic Effect

[0037] A method for catalytic synthesis of dimethyl carbonate based on a novel solid base is as follows:

[0038] 1) Dissolve 4.07 g (20 mmol) of magnesium chloride hexahydrate and 2.78 g (10 mmol) of ferrous sulfate heptahydrate in 100 mL of deionized water. After fully dissolving, add 100 mL of 0.3 M sodium oxalate aqueous solution dropwise thereto to produce a precipitate; filter and collect the precipitate, wash it thoroughly with distilled water, and vacuum dry it at 60 °C for 12 h to obtain 2.1 g of catalyst support;

[0039] 2) Add a certain amount of KF methanol solution (the mass of KF is 20% of the support) to the obtained solid, ultrasonically mix it thoroughly, let the slurry stand for 6 h, rotary evaporate to remove methanol, vacuum dry it overnight at 100 °C, and calcine it at 600 °C in a muffle furnace for 0.5-5 h to obtain about 1.8 g of solid base catalyst;

[0040] 3) Add 300 mg (5 wt.%) of catalyst, 6 g (68.14 mmol) of ethylene carbonate, and 22 mL (545 mmol) of methanol to a 100 mL round-bottom flask equipped with an electromagnetic stirrer and a reflux tube, heat to reflux, react for 2 h. After the reaction is completed and the reaction system is cooled to room temperature, take 1 mL of the reaction solution, filter it through a filter membrane, add 10 mL of methanol, and perform gas chromatography analysis.

[0041] Table 4 Influence of Different Calcination Times on the Yield and Selectivity of Dimethyl Carbonate

[0042]

[0043]

[0044] As can be seen from the data in Table 4, when the calcination time of the catalyst is 0.5 - 5 h, the product dimethyl carbonate can be obtained with good yield and selectivity. Especially when the calcination time is greater than or equal to 1 h, sufficient solid-phase reaction has occurred. Therefore, during the catalyst preparation process, the preferred calcination time of the catalyst is 0.5 - 5 h, and more preferably 1 - 2 h.

[0045] Example 5 Influence of the molar ratio of methanol to ethylene carbonate on the catalytic effect

[0046] A method for catalytic synthesis of dimethyl carbonate based on a novel solid base is as follows:

[0047] 1) Dissolve 4.07 g (20 mmol) of magnesium chloride hexahydrate and 2.78 g (10 mmol) of ferrous sulfate heptahydrate in 100 mL of deionized water. After complete dissolution, add 100 mL of 0.3 M sodium oxalate aqueous solution dropwise thereto to form a precipitate; filter and collect the precipitate, wash it thoroughly with distilled water, and vacuum dry it at 60 °C for 12 h to obtain 2.1 g of catalyst support;

[0048] 2) Add a certain amount of KF methanol solution (the mass of KF is 20% of the support) to the obtained solid, ultrasonically mix it thoroughly, let the slurry stand for 6 h, rotary evaporate to remove methanol, vacuum dry it overnight at 100 °C, and calcine it at 600 °C in a muffle furnace for 1 h to obtain about 1.8 g of solid base catalyst;

[0049] 3) Add 300 mg (5 wt.%) of catalyst, 6 g (68.14 mmol) of ethylene carbonate, and methanol (the molar ratio of methanol to ethylene carbonate is controlled at 4 - 16) to a 100 mL round-bottom flask equipped with an electromagnetic stirrer and a reflux tube, heat to reflux, react for 2 h. After the reaction ends and the reaction system cools to room temperature, take 1 mL of the reaction solution, filter it through a filter membrane, add 10 mL of methanol, and perform gas chromatography analysis.

[0050] Table 5 Influence of the molar ratio of methanol to ethylene carbonate on the yield and selectivity of dimethyl carbonate

[0051]

[0052] Since the transesterification reaction between methanol and ethylene carbonate is a reversible reaction, excessive methanol promotes the reaction equilibrium to shift towards the direction of dimethyl carbonate. As can be seen from the data in Table 5, when the alcohol-ester ratio is 1:4 - 16, relatively high yields of dimethyl carbonate can be obtained. Considering comprehensively the yield of DMC and the energy consumption in the product separation process, the alcohol-ester ratio is further preferably 1:8 - 12.

[0053] Example 6 Influence of the catalyst dosage on the catalytic effect

[0054] A method for synthesizing dimethyl carbonate based on a novel solid base catalyst, the steps are as follows:

[0055] 1) Dissolve 4.07 g (20 mmol) of magnesium chloride hexahydrate and 2.78 g (10 mmol) of ferrous sulfate heptahydrate in 100 mL of deionized water. After complete dissolution, add 100 mL of 0.3 M sodium oxalate aqueous solution dropwise thereto to form a precipitate; filter and collect the precipitate, wash it thoroughly with distilled water, and vacuum dry it at 60 °C overnight to obtain 2.1 g of catalyst support;

[0056] 2) Add a certain amount of KF methanol solution (where the mass of KF is 20% of the support) to the obtained solid, ultrasonically mix it thoroughly, let the slurry stand for 6 h, rotary evaporate to remove methanol, vacuum dry it at 100 °C overnight, and calcine it at 600 °C in a muffle furnace for 1 h to obtain about 1.8 g of solid base catalyst;

[0057] 3) Add a catalyst with a mass of 0.1 - 5 wt.% of the mass of ethylene carbonate, 6 g (68.14 mmol) of ethylene carbonate, and 22 mL (545 mmol) of methanol to a 100 mL round-bottom flask equipped with an electromagnetic stirrer and a reflux tube, heat to reflux, and react for 2 h. After the reaction is completed and the reaction system is cooled to room temperature, take 1 mL of the reaction solution, filter it through a filter membrane, add 10 mL of methanol, and perform gas chromatography analysis.

[0058] Table 6 Influence of catalyst dosage on the yield and selectivity of dimethyl carbonate

[0059]

[0060] It can be seen from the data in Table 6 that when the catalyst dosage increases from 0.1 wt.% to 5 wt.%, the yield of dimethyl carbonate increases from 43% to 88%. Due to the reversible transesterification reaction reaching thermodynamic equilibrium, further increasing the catalyst dosage has little effect on the yield and selectivity of dimethyl carbonate. Therefore, during the reaction process, the preferred catalyst dosage is 0.5 - 5 wt.%.

[0061] Example 7 Influence of reaction time on the catalytic effect

[0062] A method for synthesizing dimethyl carbonate based on a novel solid base catalyst, the steps are as follows:

[0063] 1) Dissolve 4.07 g (20 mmol) of magnesium chloride hexahydrate and 2.78 g (10 mmol) of ferrous sulfate heptahydrate in 100 mL of deionized water. After complete dissolution, add 100 mL of 0.3 M sodium oxalate aqueous solution dropwise thereto to form a precipitate; filter and collect the precipitate, wash it thoroughly with distilled water, and vacuum dry it at 60 °C for 12 h to obtain 2.1 g of catalyst support;

[0064] 2) Add a certain amount of KF methanol solution (the mass of KF is 20% of the carrier) to the obtained solid, ultrasonically mix it thoroughly, let the slurry stand for 6 h, rotary evaporate to remove methanol, vacuum dry overnight at 100 °C, and calcine at 600 °C in a muffle furnace for 1 h to obtain about 1.8 g of solid base catalyst;

[0065] 3) Add 300 mg (5 wt.%) of catalyst, 6 g (68.14 mmol) of ethylene carbonate, and 22 mL (545 mmol) of methanol to a 100 mL round-bottom flask equipped with magnetic stirring and a reflux tube, heat to reflux, and react for 0.5 - 3 h. After the reaction is completed and the reaction system is cooled to room temperature, take 1 mL of the reaction solution, filter it through a membrane, add 10 mL of methanol, and perform gas chromatography analysis.

[0066] Table 7 Effects of different reaction times on the yield and selectivity of dimethyl carbonate

[0067]

[0068]

[0069] It can be seen from the data in Table 7 that under the catalysis of the solid base, the reaction can reach a relatively high yield of dimethyl carbonate in 0.5 h. Further prolonging the reaction time has little effect on the yield and selectivity of dimethyl carbonate. Therefore, the reaction time is selected as 0.5 - 3 h, and further preferably 1 - 2 h.

[0070] Example 8 Investigation of the stability of the catalyst during recycling

[0071] A method for catalytic synthesis of dimethyl carbonate based on a novel solid base is as follows:

[0072] 1) Dissolve 4.07 g (20 mmol) of magnesium chloride hexahydrate and 2.78 g (10 mmol) of ferrous sulfate heptahydrate in 100 mL of deionized water. After complete dissolution, add 100 mL of 0.3 M sodium oxalate aqueous solution dropwise to produce a precipitate; filter and collect the precipitate, wash it thoroughly with distilled water, and vacuum dry at 60 °C for 12 h to obtain 2.1 g of catalyst support;

[0073] 2) Add a certain amount of KF methanol solution (the mass of KF is 20% of the carrier) to the obtained solid, ultrasonically mix it thoroughly, let the slurry stand for 6 h, rotary evaporate to remove methanol, vacuum dry overnight at 100 °C, and calcine at 600 °C in a muffle furnace for 1 h to obtain about 1.8 g of solid base catalyst;

[0074] 3) Add 300 mg (5 wt.%) of the catalyst, 6 g (68.14 mmol) of ethylene carbonate, and 22 mL (545 mmol) of methanol into a 100 mL round-bottom flask equipped with magnetic stirring and a reflux tube. Heat to reflux and react for 2 h. After the reaction is completed and the reaction system is cooled to room temperature, take 1 mL of the reaction solution, filter it through a membrane filter, add 10 mL of methanol, and perform gas chromatography analysis.

[0075] 4) Filter the reaction system to separate the solid catalyst and wash it with methanol. Place the catalyst in a vacuum drying oven and dry it under vacuum at 110 °C for 2 h, then calcine it in a muffle furnace at 400 °C for 1 h. Weigh and record the mass of the catalyst and use it in the next batch of reactions. After the reaction is completed, analyze the yield and selectivity of DMC.

[0076] Table 8 Stability of the catalyst during recycling

[0077]

[0078] It can be seen from the data in Table 8 that the catalytic activity decays with the weight loss of the catalyst. In the first 4 cycles, the yield of DMC remained above 79% and the selectivity remained above 90%, indicating that the catalyst is relatively stable. However, in the fifth and sixth cycles, a significant decrease in the catalyst activity was observed.

[0079] The above has described several embodiments of the present invention in detail, but the described content is only the preferred embodiments of the present invention and cannot be considered as limiting the scope of implementation of the present invention. Any equivalent changes and improvements made within the scope of the application of the present invention shall still fall within the scope covered by the patent of the present invention.

Claims

1. A method for synthesizing dimethyl carbonate based on a novel solid base catalysis, characterized in that it comprises the following steps: Step 1: adding a solid base catalyst, ethylene carbonate and methanol into a reaction container and raising the temperature to react; After the reaction in step 2 is completed, the solid catalyst is recovered by filtration to obtain a reaction mixture containing dimethyl carbonate.

2. A method for catalytic synthesis of dimethyl carbonate based on a novel solid base according to claim 1, characterized in that: The solid base catalyst is prepared by the following steps: dissolving magnesium chloride hexahydrate and ferrous sulfate heptahydrate in a certain molar ratio in deionized water, and adding a sufficient amount of sodium oxalate solution dropwise thereto under stirring conditions, filtering after metal ions are precipitated, and washing the precipitate with distilled water, and after the precipitate is fully dried, adding a certain amount of KF methanol solution to the obtained solid, fully mixing and aging, then removing methanol by a suitable method, and calcining at high temperature to obtain the solid base catalyst.

3. A method for catalytically synthesizing dimethyl carbonate based on a novel solid base according to claim 1 and claim 2, characterized in that: When preparing the solid base catalyst, the molar ratio of magnesium chloride hexahydrate to ferrous sulfate heptahydrate is 1:0.5-2, the mass of KF is 10-30% of the precipitate, the high-temperature calcination temperature ranges from 200 to 700°C, and the calcination time is 0.5 to 5 hours.

4. A method for synthesizing dimethyl carbonate based on a novel solid base catalyst according to claim 1 and claim 2, characterized in that: In the reaction of synthesizing dimethyl carbonate, the amount of solid base catalyst added is 0.1-5% of the mass of ethylene carbonate, the molar ratio of methanol to ethylene carbonate is 1:4-16, and the reaction time is 0.5-3h.

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